TSE bug with ff_tx_mod = 3?

Hi, did anyone see a problem with the TSE ethernet core when ff_tx_mod = 3? I tested my design, it works fine for ff_tx_mod = 0, 1, 2 but not 3. tcpdump shows 1 or 2 bytes missing. I checked it on SignalTAP and all the signals of TX seem to be OK. Here is my configuration:

board: Cyclone IV GX starter kit
Protocol: UDP
Quartus version: 12.1

Thanks,
Mark